1. Field of the Invention
The invention pertains generally to detection devices utilizing ionization sensor cells for monitoring gaseous media and for detecting changes in the compositional characteristics thereof. In more particular respects, the present invention relates to a process and apparatus for rendering such devices more suitable for reliable field-use, and particularly more suitable for personal field-use for the detection of changes in the normal compositional characteristics of the ambient atmosphere such as may result, for example, from the presence in the ambient atmosphere of dangerous or harmful substances.
2. Description of the Prior Art
Heretofore, ionization sensor cells commonly have been used in detector units for detecting the presence of harmful gases and vapors. Moreover, such detector units have commonly utilized one or more such cells for testing sample gas and vapors fed thereto by aspirator pumps. Additionally, such detector units have conventionally included supplemental electronic elements such as amplifiers, recorders, etc., to set off or activate one or more warning alarms in response to the detection of harmful gases and/or vapors sensed to be present in excess of a preselected concentration level.
In the past, before my invention, it was found that when variations in the rate of flow of the gas or vapor being detected occurred, erratic changes or fluctuations in the electrical output signals emitted by the sensor cell took place which, of course, interfere with and obstruct the reliability of any output signal characteristics which are attributable to the composition of the medium being monitored. Consequently, the detector unit was not adequately reliable for its intended purpose and false alarms were not uncommon.
Various corrective measures were taken. The sensor cell outputs were placed in opposition to each other so that a cancellation effect would occur. Although this technique, adopted by the U.S. Air Force, has met with marginal success, it has required the use of an excessive number of cells, amplifiers and accessory components, as well as undesirably high power supplies which ordinarily are not available from small, lightweight power sources. Consequently, the detector units were inordinately heavy, bulky and unsuitable for use as a lightweight, portable device for personal field-use. Moreover, high voltages on the terminals were commonplace.